The HSV-1 capsid is comprised of seven proteins that together form a large complex assembly. The intimate association of these proteins to create a protective shell around the virus genome requires multiple protein-protein interactions. These interactions drive the assembly of this structure. Assemblies of large protein complexes are evident in a number of cellular systems including transcription, protein translation, and protein degradation. Thus, defining how these multi-protein assemblies associate, interact and characterization of their structural features is a fundamental problem in biology. The protein coat that protects the virus genomes has been studied as a paradigm for how proteins interact and self-assemble into higher order structures. This proposal addresses the interactions between the HSV-1 capsid proteins, and the residues that mediate these interactions. The structural features of these multi-protein complexes will be analyzed from isolated complexes and in the context of the capsid shell. The validation of an antiviral target depends on the information gained from identification of interactive domains and their structural characteristics. [unreadable] [unreadable] Specific Aim 1. Identify the residues in the hydrophobic "pocket" or surface in the N-terminus of VP5 that bind to the C-terminus of the scaffold protein (22a). Evaluate the antiviral potential of this interaction using peptides that mimic this domain to inhibit protein-protein binding and capsid assembly. Determine the minimal N-terminal protein fragment ofVP5 that can still bind to the C-terminal tail of 22a and characterize the structural properties of this complex. [unreadable] Specific Aim 2. Use genetic methods to confirm an essential structural function encoded by the HSV-1 protease (VP24) during capsid maturation. Characterize this second function and use protein-domain swapping experiments to identify the region of VP24 critical for this function. [unreadable] Specific Aim 3. Identification of the residues of VP23 that are required for interaction with VP19C during triplex assembly; for self-interaction during dimer formation; and for interaction with VP5 during capsid assembly and re-configuration of the shell. [unreadable] Specific Aim 4. Identify using electron cryo-microscopy and 3D image reconstruction the location of the N-terminus of VP26 and VP19C in the capsid shell. Determine the location of the largest tegument protein, VPI/2, in the capsid shell. [unreadable] [unreadable]